1. Field of the Invention
This invention relates generally to fluid actuators and more particularly to a composite cylinder for use in hydraulic actuators intended for aircraft flight controls.
2. Prior Art
Fluid actuators of the type used in flight controls for aircraft and other high pressure applications are required to withstand high impulse pressures without failing over extended periods of time. In the prior art, to insure that the actuator had the necessary strength, common practice has been to construct the actuator cylinder out of a monolithic metal piece. Such structure adds considerably to the weight of the actuator.
To provide actuator cylinders having lighter weight than those constructed with a monolithic metal piece but at the same time providing adequate strength, the use of a composite cylinder has been suggested. Typical of such composite cylinders are those disclosed in prior art U.S. Pat. Nos. 4,685,384, 4,697,499, 4,802,404, and 4,773,306. The composite cylinders disclosed in these patents include a metal liner which is wound with hoop windings made of a suitable composite fiber such as a graphite filament impregnated with a suitable resin. The filaments, in addition to being hoop wound, have also been helically wound, and in some instances, disposed in longitudinal winding form. The combination of the hoop, helical and longitudinal windings provide the ability for the composite cylinder to react to circumferential loads, axial loads and compressive loads generated in the cylinder during the operation of the hydraulic actuator.
Although such composite cylinders have functioned quite well for the purposes intended, difficulties have been experienced in that the windings are incapable of supporting the loads encountered in all instances. Such difficulties have been generated because of the manner of retaining the wound filaments on the liner and particularly on the metal end glands necessary for receiving end plates which in turn receive the piston rods or clevis attachment members necessary for proper operation of the hydraulic actuator.